Murderer tried to frame his own brother

John Garda's body was found buried in a shallow grave. Photo: Supplied: David Goldman

A man who slit a Byron Bay businessman's throat and then blamed his own brother has been jailed for at least 21 years for the "inexplicable" murder.

The truth about the death of 60-year-old John Garda, whose body was discovered in a shallow grave at Broadwater on the far north coast in February 2010, may never be known, Justice Ian Harrison said in the NSW Supreme Court on Friday.

Kevin Malcolm Purtill, 41, from Lennox Head, was sentenced to a maximum term of 28 years' imprisonment for the murder, which the judge found occurred during a drug transaction at Purtill's home on February 8, 2010.

A jury found Purtill guilty despite his assertions that he was innocent and that his brother, Warren Purtill, was the killer.

The trial heard Mr Garda, a well-known Byron Bay convenience store owner, came to Kevin Purtill's home on the afternoon of the murder and a fight broke out.

Warren Purtill was downstairs watching a DVD with a neighbour and the court heard he ran upstairs when he heard the noise.

The neighbour told the court she fled the scene after she saw blood dripping through her ceiling from the unit above.

Testifying against his brother, Warren Purtill said there was "blood everywhere" when he entered the unit and Mr Garda was lying dead on the floor.

He said his brother had asserted Mr Garda was trying to kill him.

Warren Purtill said he agreed to dispose of the body and clean the unit, while Kevin Purtill left for Brisbane.

He pleaded guilty to being an accessory after the murder and was jailed for at least three years last May.

Kevin Purtill told the court that he left his home when Warren entered and that Warren then killed Mr Garda - an account Justice Harrison said was "frankly incredible".